Oh, this was fun and exciting to "create" my first markdown-lint rule - https://github.com/aepfli/markdownlint-rule-max-one-sentence-per-line

based on the work from @JoshuaKGoldberg and with a lot of valuable feedback from @DavidAnson within https://github.com/DavidAnson/markdownlint/pull/719

Feedback is highly appreciated :)